Fabrication of trapezoidal pole for magnetic recording

ABSTRACT

A method for forming a magnetic write pole with a trapezoidal cross-section is described. The method consists of first forming a magnetic seedlayer on a base followed by depositing a removable material layer on the seedlayer, and then a resist layer on the removable material layer. A trench is then formed in the resist, and the resist is heated to cause the cross-sectional profile of the trench to assume a trapezoidal shape. The resist is then capped with another resist layer and further heated to cause the width of the trapezoidal trench to become narrower. The cap layer and removable material layer at the bottom of the trench are then removed and the trench filled with magnetic material by electroplating. The resist and seedlayer external to the trench are finally removed to form a write pole with a trapezoidal cross-section.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with United States Government support underAgreement No. 70NANB1H3056 awarded by the National Institute ofStandards and Technology (NIST). The United States Government hascertain rights in the invention.

FIELD OF THE INVENTION

The invention relates to magnetic recording heads and more particularlyto the fabrication of a trapezoidal write pole.

BACKGROUND

Magnetic recording heads have utility in a magnetic disc drive storagesystem. Most magnetic recording heads used in such systems today are“longitudinal” magnetic recording heads. Longitudinal magnetic recordingin its conventional form has been projected to suffer fromsuperparamagnetic instabilities at densities above approximately 40Gbit/in². It is believed that reducing or changing the bit cell aspectratio will extend this limit up to approximately 100 Gbit/in². However,for recording densities above 100 Gbit/in², different approaches willlikely be necessary to overcome the limitations of longitudinal magneticrecording.

An alternative to longitudinal recording that overcomes at least some ofthe problems associated with the superparamagnetic effect is“perpendicular” magnetic recording. Perpendicular magnetic recording isbelieved to have the capability of extending recording densities wellbeyond the limits of longitudinal magnetic recording. Perpendicularmagnetic recording heads for use with a perpendicular magnetic storagemedium may include a pair of magnetically coupled poles, including amain write pole having a relatively small bottom surface area and a fluxreturn pole having a larger bottom surface area. A coil having aplurality of turns is located adjacent to the main write pole forinducing a magnetic field between the pole and a soft underlayer of thestorage media. The soft underlayer is located below the hard magneticrecording layer of the storage media and enhances the amplitude of thefield produced by the main pole. This in turn allows the use of storagemedia with higher coercive force. Consequently, more stable bits can bestored in the media. In the recording process an electrical current inthe coil energizes the main pole, which produces a magnetic field. Theimage of this field is produced in the soft underlayer to enhance thefield strength produced in the magnetic media. The flux density thatdiverges from the tip into the soft underlayer returns through thereturn flux pole. The return pole is located sufficiently far apart fromthe main write pole such that the material of the return pole does notaffect the magnetic flux of the main write pole, which is directedvertically into the hard layer and the soft underlayer of the storagemedia.

A magnetic recording system such as, for example, a perpendicularmagnetic recording system may utilize a write pole with a square orrectangular cross-section. Under certain circumstances, the increasedmagnetic field concentration at the sharp corners can cause writing orerasure on adjacent tracks.

Another development that overcomes at least some of the problemsassociated with the superparamagnetic effect is heat assisted magneticrecording (HAMR), sometimes referred to as optical or thermal assistedrecording. Heat assisted magnetic recording generally refers to theconcept of locally heating a recording medium to reduce the coercivityof the recording medium so that the applied magnetic writing field canmore easily direct the magnetization of the recording medium during thetemporary magnetic softening of the recording medium caused by the heatsource. The heat assisted magnetic recording allows for the use of smallgrain media, which is desirable for recording at increased aerialdensities, with a larger magnetic anisotropy at room temperature andassuring a sufficient thermal stability.

More specifically, super paramagnetic instabilities become an issue asthe grain volume is reduced in order to control media noise for highaerial density recording. The superparamagnetic effect is most evidentwhen the grain volume V is sufficiently small that the inequalityK_(u)V/k_(b)T>40 can no longer be maintained. K_(u), is the magneticcrystalline anisotropy energy density of the material, k_(b) isBoltzman's constant, and T is absolute temperature. When this inequalityis not satisfied, thermal energy demagnetizes the individual grains andthe stored data bits will not be stable. Therefore, as the grain size isdecreased, in order to increase the aerial density, a threshold isreached for a given material K_(u), and temperature T such that stabledata storage is no longer feasible.

The thermal stability can be improved by employing a recording mediumformed of a material with a very high K_(u). However, with the availablematerials, the recording heads are not able to provide a sufficient orhigh enough magnetic writing field to write on such a medium.Accordingly, it has been proposed to overcome the recording head fieldlimitations by employing thermal energy to heat a local area on therecording medium before or at about the time of applying the magneticwrite field to the medium. By heating the medium, the K_(u), or thecoercivity is reduced such that the magnetic write field is sufficientto write to the medium. Once the medium cools to ambient temperature,the medium has a sufficiently high value of coercivity and assuresthermal stability of the recorded information. When applying a heat orlight source to the medium, it is desirable to confine the heat or lightto the track where writing is taking place, and to generate the writefield in close proximity to where the medium is heated to accomplishhigh aerial density recording. The separation between the heated spotand the write field spot should be minimal or as small as possible sothat the writing may occur while the medium temperature is substantiallyabove ambient temperature. This also provides for the efficient coolingof the medium once the writing is completed.

Accordingly, there is identified a need for an improved write pole witha shape and dimensions that overcome the limitations and shortcomings ofknown magnetic recording heads and heat assisted magnetic recordingheads.

SUMMARY

In one aspect of the invention, a method of forming a magnetic writepole with a trapezoidal cross-section is presented. The method comprisesforming a magnetic seedlayer on a base, forming a removable materiallayer on the seedlayer, forming a resist layer on the removable layerand forming a trench in the resist and heating the structure for a firstamount of time at a first temperature to form a predetermined slope inthe first and second sidewalls of the trench. The method furthercomprises capping the trench with another resist layer and heating thecapped trench for a second amount of time at a second temperature toshrink the separation of the first and second sidewalls of the trench,removing the cap layer and the removable material at the bottom of thetrench, electroplating a magnetic material in the trench and removingthe resist by stripping the resist and finally removing the seedmaterial outside the pole area by ion-beam etching to form the magneticpole.

In accordance with another aspect of the invention, a magnetic writepole with a multilayer structure and a trapezoidal cross-sectioncomprises a base and a multilayer magnetic seedlayer on the base. Amagnetic layer on the seedlayer has a trapezoidal cross-section, abottom width W_(b) less than or equal to about 100 nm, a top width ofabout 1.25 to 3 times W_(b), a height h, and an aspect ratio h/W_(b) ofabout 1:1 to about 10:1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view from the air bearing surface (ABS)plane showing a prior art HAMR write pole.

FIG. 1B is a cross-sectional view from the ABS plane showing atrapezoidal write pole of the current invention.

FIG. 2 is a diagram illustrating the steps to form a trapezoidal pole.

FIG. 3 is a cross-sectional view of a trench in a resist layer on asubstrate before (A) and after (B) a thermal bake process.

FIG. 4 is a cross-sectional view of a capped trench in a resist layer ona substrate before (A) and after (B) a thermal shrink process. Theresist cap is removed in (C).

FIG. 5A are SEM images showing different trench profiles achieved atdifferent temperatures during thermal bake process. FIG. 5B is a graphshowing bottom and top spacing and beveled angle as a function of baketemperature.

FIG. 6A are SEM images showing different trench profiles after bakingfor different times. FIG. 6B is a graph showing bottom and top spacingand beveled angle as a function of bake time.

FIG. 7 are SEM images showing trench profiles after combinations ofthermal bake (Process A) and thermal shrink (Process B).

FIG. 8 are SEM images showing trench profiles after combinations ofthermal bake (Process B) and thermal shrink (Process A).

FIG. 9 is a cross-sectional view of resist layer 300 on easily removableresist layer 290 on magnetic seed layer 210 on substrate 220 (not toscale).

FIG. 10A are magnetic hysteresis loops for a 1000 Å single CoNiFe layer.

FIG. 10B are magnetic hysteresis loops for a 1000 Å laminated seedlayerwith a Ni₈₀Fe₂₀ cap layer.

FIG. 11 is a chart of corrosion resistance of CoNiFe seedlayers with andwithout Ni₈₀Fe₂₀ cap layer.

FIG. 12 are SEM images of 100 nm wide plated trapezoidal poles using (a)a CoNiFe seedlayer and (b) a CoNiFe seedlayer with Ni₈₀Fe₂₀ anticorrosion cap layer.

FIG. 13 is a diagram illustrating the steps to electroplate magnetictrapezoidal pole.

FIG. 14 is a schematic of an Ms gradient trapezoidal pole configuration.

FIG. 15 is a cyclic voltammetry plot of current density versus appliedpotential for the single bath electrolyte shown in Table 2.

FIG. 16 is a graph showing how composition and magnetic moment of aplated pole can be tailored by adjusting plating current density for thesingle bath electrolyte shown in Table 2.

FIG. 17 are SEM images of the microstructures of 0.5T NiCu (left) and0.3T NiCu (right) plated from the single bath shown in Table 2.

FIG. 18 are magnetic hystresis loops of a plated graded Ms stackcontaining a CoNiFe laminate seed.

FIG. 19A is a schematic of a trapezoidal pole before seed removal.

FIG. 19B is a schematic of a trapezoidal pole after seed removal.

FIG. 20 is a FIB-SEM image of a cross-sectioned trapezoidal pole afterseed removal.

FIG. 21 is a schematic of a static ion beam etch method.

FIG. 22 is a SEM image of a cross-sectioned trapezoidal pole after seedremoval by static ion beam etch.

FIG. 23 is a SEM image of a cross-sectioned trapezoidal pole afterbackfilling with Comptech sputtered alumina.

FIG. 24 is a SEM image of a cross-sectioned trapezoidal pole afterbackfilling with IBD aluminum.

FIG. 25 are SEM images of sectioned (top row) and unsectioned (bottomrow) trapezoidal poles with three different designs.

DETAILED DESCRIPTION

The present invention relates to the problem of side writing or erasureon adjacent tracks due to magnetic field concentrations at sharp cornersin prior art write poles with rectangular cross-sections as seen fromthe air bearing surface (ABS) of a recording media. FIG. 1A shows across-section of prior art write pole 10 as seen from the ABS. Writepole 10 has three sections, 20, 30, and 40. The shading on FIG. 1illustrates magnetic field concentrations capable of side writing orerasure. The embodiment of the invention is to replace sections 20 and30 with a single pole 50 having a trapezoidal cross-section with abottom spacing 70 at its tip and a top spacing 80 to form write pole 60as shown in FIG. 1B. Furthermore, by making the spacing of section 90 inFIG. 1B equal to top spacing 80, the corners responsible for magneticfield leakage are eliminated. In another embodiment of the invention,the aspect ratio H/W of the trapezoidal pole 50 is about 1:1 to about10:1 to keep the wider portions away from the bottom edge (front edge)of the pole that does the writing. In another embodiment of theinvention, the magnetization of the trapezoidal pole 50 is graded toensure that the field from the top of the pole is lower than the fieldfrom the bottom of the pole since writing is done at the bottom of thepole.

Prior art trapezoidal poles have been fabricated using high angleion-beam etching with masking to create the trapezoidal shape. Thisprocess is not compatible with the process used to form heat assistedmagnetic recording (HAMR) heads. A process that is compatible with theHAMR process is electroplating in a resist trench with a trapezoidalshape.

The disclosed invention solves the following issues. 1) The trench has atrapezoidal shape. 2) The trench width at the bottom is less than 100nm. 3) The aspect ratio W/H is about 1:1 to about 10:1. 4) Removing theseedlayer without leaving a footing or redepositing seedlayer materialon the sides of the pole. 5) Backfilling with alumina without leavingvoids in the alumina. 6) The process needs to be compatible withstandard processes in industry fabs.

The invention discloses how to form a narrow trench with a controlledtrapezoidal shape and controllable top and bottom separations. Insummary the method is a hybrid thermal flow process consisting of aresist post-development thermal bake treatment process that allows asub-100 nm high aspect ratio trench with a trapezoidal shape to beformed that can then be used as a template for electroplating writerpole materials.

Lithographic Process

The steps to form a magnetic pole with a trapezoidal cross-section aregiven in FIG. 2. First, a substrate is provided (step 100). Thesubstrate can be a ceramic composite used to form sliders such as analuminum oxide/titanium oxide composite or other materials known in theart. A plating seedlayer is deposited on the substrate (step 102).Suitable seedlayers are selected from a group but are not limited toFeCo, NiFe, CoNiFe, Ru, Ta, CoZrTa, CoNbTa, and Cu.

A thin, easily removable, resist layer is deposited on the seedlayer(step 104). The removable layer is preferably about 10 nm to about 30 nmthick and is preferably a polymethylglutarimide (PMGI) layer. Theremovable layer is then given a post-apply bake (step 106). A thickertop resist layer is then deposited on the PMGI layer with a thickness offrom about 0.5 μm to about 4.0 μm depending on the requirements for thetop pole design (step 108). The resist is then given a post-apply bake(step 110). The resist is then exposed using e-beam or otherlithographic tools e.g. G-line, I-line, DUV, 193 nm scanner, electronbeam direct write, EUV, x-ray lithography or others (step 112). Theexposed wafer is then given a post exposure bake (step 114). The exposedwafer is then developed in standard tetramethyl ammonium hydroxide(TMAH) developer to form a rectangular trench (step 116). The developedwafer is then put through a hybrid thermal flow process, describedlater, to produce the proper trapezoidal shape and spacing of the trench(step 118). Magnetic material is then electroplated in the trench toform a magnetic trapezoidal pole (step 120).

Hybrid Thermal Flow Process

The hybrid thermal flow process is composed of two processes, a thermalbake process and a thermal shrink process. In the thermal bake process,the resist is baked at a temperature close to the glass transitiontemperature, Tg, of the resist. This causes the walls of the trench toslope into a trapezoidal cross-section as shown in FIG. 3. FIG. 3A showsresist layer 220 with trench 221 on substrate 230 before thermal bakeprocess. FIG. 3B shows resist layer 220 after thermal bake. Trench 221with rectangular cross-section has transformed into trench 222 withtrapezoidal cross-section after the bake.

The thermal shrink process is illustrated in FIG. 4 where resist layer240 on substrate 230 with a rectangular trench is capped with resistlayer 242. Resist layer 242 is applied by spin coating and fills thetrench during the process. The spacing of the trench is “a”. The resistis then baked at a temperature less than, equal to, or greater than thatused for the thermal bake process. This thermal shrink process causesthe separation of the two walls of the trench to decrease giving anadded dimension to the control of the trapezoidal trench formingprocess. The new spacing is “b” where b<a. The thermal shrink processcan be repeated at will to obtain the required trench separation. Thethermal bake process and thermal shrink process can be interchanged asneeded to obtain required trapezoidal trench shapes and dimensions. Bycombining the two processes, trenches with high aspect ratios of 1:1 to10:1 and sub-100 nm spacing have been produced. The process is verymanufacturable. The addition of the hybrid thermal bake process to anoverall manufacturing process can be done using resist development tracktools that are standard in most industry fabs. The actual time it takesto incorporate these processes into the lithographic step is minimalcompared to the results that can be achieved. In addition, the cost ofthe added material is attractively small in relation to the cost ofupdating and maintaining advanced lithographic equipment such as DUV,193 nm scanners, electron beam direct write, or EUV tools that areneeded to reduce trench dimensions to the sub-100 nm regime. It shouldbe mentioned that this method or process is not limited to theapplication of magnetic pole fabrication. In principle it can be used inany device fabrication in the case where a narrow trapezoidal trenchpattern is needed.

An example of how a trapezoidal shape is formed in a 1.3 μm thick resistwith a rectangular trench during a thermal bake is shown in FIG. 5A.Scanning electron microscope (SEM) images of the trench are shown atdifferent temperatures after a 60 second bake at different temperaturesin FIG. 5A. The bottom and top spacing, of the trench as well as thebevel angle are shown in FIG. 5B as a function of temperature for a 60second baking time. The top spacing and bevel angle are smoothly varyingfunctions of temperature while the bottom spacing remained constant.

FIGS. 6A and 6B show the time dependence of the thermal bake process at145° C. on trench dimensions in a 1.3 μm thick resist. The top spacingand bevel angle are smoothly varying functions of time while the bottomspacing remained constant. Combinations of the thermal bake process andthe thermal shrink process can give considerable latitude to the shapingof a trapezoidal trench.

FIG. 7 shows SEM images of trenches in a 1.3 μm thick resist given threeexposures (increasing from top to bottom). Process A was a thermal bakeat 155° C. for 60 seconds and process B was a thermal shrink process at120° C. for 90 seconds. The shrinking of the wall separation aftermultiple thermal shrink treatments (A+B, A+2B, A+3B, and A+4B) isevident. Other combinations of treatments were carried out with similarresults.

FIG. 8 shows trapezoidal shape formation in a 1.3 μm thick resist giventhree exposure levels again. In this case the originals were given twothermal shrink treatments (Process B) of 60 seconds each at 120° C. andthen given one thermal bake treatment (Process A) for 90 seconds at 130°C., 140° C., and 150° C. The large control over the shape of the trenchis obvious.

Plating Process

The plating process to form a trapezoidal pole starts with step 102 inFIG. 2, deposit seedlayer. Although the seedlayer used in this processis described in detail, other seedlayers and combinations of seedlayerscan be used. A schematic showing the layer structure of the seed andresist layers is shown in FIG. 9 where the relative dimensions are notto scale. All layers in seedlayer 310 can be formed by physical vapordeposition (PVD), e-beam vapor deposition, sputtering and other meansknown to those in the art. The seedlayer has two characteristics, alaminated layer structure and an anticorrosion cap. Seedlayer 310 isshown on substrate 320 and includes first or bottom layer 330 onsubstrate 320. First layer 330 is NiFe about 15 Å thick. Second layer340 is CoNiFe about 350 Å thick. Third layer 350 on CoNiFe layer 340 isTa about 12 Å in thickness. Fourth layer 360 includes three NiFe layersabout 15 Å thick each. Fifth layer 370 on NiFe layer 360 is CoNiFe about250 Å thick. Sixth or cap layer 380 is Ni₈₀Fe₂₀ about 50 Å thick and isadded for anticorrosion protection as will be discussed below. Easilyremovable resist layer 390 is on cap layer 380. Layer 390 is preferablya PMGI layer about 10 nm to 30 nm thick and is applied to protect theseedlayer at the base of the trench during subsequent thermalprocessing. Thick resist layer 400 is on thin easily removable layer390. Resist layer 400 is from 0.5 μm to 4.0 μm thick depending on therequirements of the pole design.

Magnetic properties of laminate seedlayer 310 are compared with a singleCoNiFe layer in FIGS. 10A and 10B. FIG. 10A shows B versus H hysteresisloops for a solid 1000 Å CoNiFe film and FIG. 10B shows B versus Hhysteresis loops for a 1000 Å laminate film. The hard axis loop of thelaminate shows almost no hysteresis.

In another embodiment of this invention, the magnetization of eachmagnetic layer in the seedlayer can be different such that the seedlayerexhibits a vertical magnetization gradient which can contribute to themagnetization gradient in the write pole.

FIG. 11 shows the corrosion resistance of a capped seedlayer to besuperior to that of an uncapped layer. This corrosion protection isimportant in defining the shape of the pole. The formation of thetrapezoidal resist shape as shown earlier involves thermal baking andshrinking which results in undercut features at the resist/seedlayerinterface. During the pre-plate and plating processes, the corrosiveplating solution can be trapped in this crevice and cause corrosion.This is evident in FIG. 12 which shows SEM images of 100 nm wide platedtrapezoidal poles using a CoNiFe seedlayer without (a) and with (b)Ni₈₀Fe₂₀ anticorrosion cap 280. The SEM images on the right were takenafter the poles were sectioned to show the trapezoidal shape. With theNi₈₀Fe₂₀ cap layer 280, the corrosive solution trapped in thephotoresist could not visibly corrode the seedlayer. Since the platingprocess is on top of an intact (uncorroded) seedlayer, the polemorphology is visibly improved and the depression in the center of thepole is eliminated.

Trapezoidal Pole Plating

The plating process flow to form a trapezoidal pole is shown in FIG. 13which shows the steps to electroplate a magnetic trapezoidal pole. Atstep 500, removable layer 390 at the bottom of the trench is removed toexpose the seedlayer. This is carried out by O₂ reactive ion etching toclear trench bottom. Next, etching removes surface oxide on theseedlayer (step 502). An acid spray etch performs this process. At step504, the trench is filled with magnetic material by electroplating.Solid FeCoNi, FeCo and graded magnetization poles can be formed.Following electroplating, the plated trench is rinsed and dried toremove plating solution (step 506). In the next step, the photoresist isremoved by oxygen ashing and solvent stripping (step 508). As discussedlater, in the final step, the exposed seedlayer is removed by ion beametching (step 510).

The solid CoNiFe pole is electroplated using the parameters shown inTable 1.

TABLE 1 Solid CoNiFe trapezoidal pole plating chemistry and parameters.Chemical Concentration (g/l) and parameters NiCl₂•6H₂O 40 CoCl₂•6H₂O 31FeCl₂•4H₂O 4 H₃BO₃ 40 NH₄Cl 40 STJ additive 0.65 Sodium LaurlelSulfate0.1 (SLS) PH 2.8 Current 2.8-3 mA/cm²

Referring to Table 1, the organic STJ additive acts as a leveling agentand plays an important role in controlling the grain size and surfacemorphology of the plated pole. Its adsorption to the narrow trenchsurface can be preferentially enhanced due to radial transportation atthe current crowding points thereby increasing plating uniformity. Dueto the trapezoidal profile of the trench cross-section, theaccessibility of the small trench by the diffusing metal ions can beincreased. This improves the uniformity of the plated pole cross-sectionalong the length of the pole.

Graded Ms Poles

As illustrated in FIG. 1A, prior art poles 10 are solid, plated, high MsCoFeNi material for sections 20, 30, and 40. This high Ms configurationresults in a magnetic field spike at the back of the pole 10. In orderto reduce this field spike, trapezoidal poles with an Ms gradient can beemployed. A schematic of a trapezoidal graded Ms pole is shown in FIG.14.

Three different pole materials with different magnetization can beplated to form this pole. For example, in the current seedlayerconfiguration (sputtered Si on substrate)/NiFe 15 Å/CoNiFe 250 Å/Ta 12Å/NiFe 15 Å)₃/CoNiFe 250 Å/Ni₈₀Fe₂₀ 50 Å, it is possible to subsequentlyplate 100 nm of IT NiFe layer using a regular NiFe bath, and 50 nm of0.5T NiCu on the IT NiFe layer, and 50 nm of 0.3T NiCu layer on the 0.5TNiCu layer using another bath.

The 0.3T and 0.5T NiCu layers can be plated from a single bath using thenovel developed bath chemistry shown in Table 2.

TABLE 2 0.3T and 0.5T NiCu plating chemistry and parameters. ChemicalConcentration (g/l) and parameters NiCl₂•6H₂O 119 CuSO₄•5H₂O 0.5 Sodiumcitrate dehydrate 29.4 H₃BO₃ 25 STJ additives 0.6 SLS 0.1 PH 55 Current(0.3T/0.5T) 2.5/10 mA/cm²

In the single bath method, deposition is carried out using a singleelectrolyte while varying deposition parameters such as voltage orcurrent to produce compositional, structural and magnetic modulations ofthe plated structure. For example, current density is shown as afunction of applied voltage in cyclic voltammetry measurements madeusing the bath given in Table 2 where ions of two metals, Cu and Ni,with Cu being more noble than Ni, are present. At certain potentials (orcurrents) that are sufficiently negative, Cu will be reduced and Ni willnot. In this region, region I in FIG. 15, Cu will be plated and Ni willnot. As the potential is decreased into region II, both Cu and Ni willplate and the amounts of each will depend on the applied potential. Asshown in FIG. 15, a 0.3T NiCu alloy will plate at a current density ofabout −2.5 mA/cm² and a 0.5T NiCu alloy will plate at a current densityof −10.0 mA/cm². Since the deposition rate of Cu is diffusion limitedand hence constant, by varying the potential (or current) duringplating, composition and magnetic modulations of the plated structurecan be achieved.

The current control technique is employed in the wafer scale embodimentdescribed here. FIG. 16 shows the composition and magnetic momentvariation in NiCu plated layers as a function of plating current. Asshown in the figure, the magnetic moment, Bs, can be convenientlytailored by adjusting the plating current. Specifically, 2.5 and 10mA/cm² currents can be applied to obtain 0.3T and 0.5T NiCu. Thecomposition uniformity (1 a) for 0.5T and 0.3T NiCu plated layers are0.1 ^(at)/₀ (0.5T) and 0.7 ^(at)/₀ (0.3T) respectively.

The microstructure of the 0.5T and 0.3T NiCu are shown in FIG. 17 ascharacterized by scanning electron microscopy (SEM). The surface lookssound and glossy and the grains are refined due to the use of the STJorganic additive in the bath. The magnetic hysteresis loop of an actualrated Ms stack is shown in FIG. 18. The stack consists of 50 nm of 0.3TNiCu on 50 nm of 0.5T NiCu on 100 nm of IT NiFe on 100 nm of CoNiFelaminate seed.

Seed Removal and Pole Backfilling

FIG. 19A is a schematic of the trapezoidal pole before ion beam etching.FIG. 19B is a schematic of the trapezoidal pole after ion beam etching.FIG. 19B indicates that the seed material redeposits on the sidewalls ofthe pole when standard rotating ion mill etching procedures are used.FIG. 20 shows a focused ion beam scanning electron micrograph (FIB-SEM)of a cross-sectioned trapezoidal pole after seed removal by the standardrotating beam ion mill etching process. The redeposited layer isindicated by the dashed lines.

A seed removal method that works best is a static etch with the waferstationary with the poles at a 30° angle with respect to the ion beam(i.e. α=30°) as shown in FIG. 21. In another embodiment, the wafer canbe swept through a range of angles e.g. from about 20° to about 40°. Asshown in the figure, the wafer is also set at 50° (i.e. θ=50°) to theion beam.

Successful seed removal using this process is shown in FIG. 22. FIG. 22is an SEM image of a seed with an 86° wall angle with no redepositedseed material on the wall of the seed. The bottom, middle and top widthsof the pole are 90 nm, 130 nm and 185 nm respectively.

Conventional sputtering such as with Alcatel Comptech equipment cannotbe used to backfill the pole with alumina. FIG. 23 is an SEM image of apole that was backfilled with sputtered alumina using Comptechequipment. There are voids along the sides of the pole as indicated bythe arrows. However, ion beam deposition can be used to backfill thepole. FIG. 24 shows two magnifications of SEM images of a polebackfilled with 1.2 μm of ion beam deposited (IBD) alumina deposited atθ=60° with the wafer rotating. There are no voids in the alumina.

EXAMPLE

SEM images of three trapezoidal poles with different dimensions thathave been fabricated by the invention disclosed herein are shown in FIG.25. The top images are end-on views of vertical cross-sections of thepoles. The bottom images are perspective views of the unsectioned poles.The bottom and top widths (i.e., critical dimension or CD) are indicatedon the figure.

In summary, a novel hybrid thermal flow method to form trapezoidal shaperesist trench structures has been invented that allows the production oftrapezoidal write poles by electroplating. This process has been used tomanufacture heat-assisted magnetic recording heads (HAMR).

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A method of forming a magnetic write pole, the method comprising:forming a magnetic seedlayer on a base; forming a removable materiallayer on the seedlayer; forming a resist layer on the removable layer;forming a trench in the resist and heating the structure for a firstamount of time at a first temperature to form a predetermined slope inthe first and second sidewalls of the trench; capping the trench withanother removable layer; heating the capped trench for a second amountof time at a second temperature to shrink the separation of the firstand second sloped sidewalls of the trench; removing the cap layer;removing the removable material at the bottom of the trench;electroplating a magnetic material in the trench; and removing theresist and seed material outside the pole area.
 2. The method of claim1, wherein the magnetic seedlayer is a multilayer seedlayer formed ofmagnetic and nonmagnetic layers.
 3. The method of claim 2, wherein themagnetic seedlayer comprises a first NiFe layer on the base, a secondCoNiFe layer on the first NiFe layer, a third Ta layer on the secondCoNiFe layer, a fourth NiFe layer on the third Ta layer, and a fifthCoNiFe layer on the fourth NiFe layer.
 4. The method of claim 3, whereinthe first NiFe layer has a thickness between about 5 Å and about 25 Å,the second CoNiFe layer has a thickness between about 150 Å and about350 Å, the third Ta layer has a thickness between about 5 Å and about 20Å, the fourth CoNiFe layer has a thickness between about 15 Å and about60 Å, and the fifth CoNiFe layer has a thickness between about 200 Å andabout 300 Å.
 5. The method of claim 3, wherein the magnetic seedlayercomprises a sixth corrosion protection layer on the fifth CoNiFe layer.6. The method of claim 5, wherein the sixth layer comprises Ni₈₀Fe₂₀. 7.The method of claim 6, wherein the sixth layer has a thickness betweenabout 25 Å and about 75 Å.
 8. The method of claim 2, wherein themagnetic layers in the magnetic seedlayer have different magnetizationssuch that the magnetic seedlayer exhibits a magnetization gradientperpendicular to the base.
 9. The method of claim 1, wherein theremovable layer on the magnetic seedlayer is a removable positive toneresist such as polymethylglutarimide (PMGI) layer having a thickness offrom about 10 nm to about 30 nm.
 10. The method of claim 1, wherein thetrench is formed in the resist by a photolithographic process.
 11. Themethod of claim 1, wherein the first temperature is close to the glasstransition temperature of the resist and the second temperature is lowerthan, about equal to or higher than the first temperature.
 12. Themethod of claim 1, wherein the magnetic pole material in the trench isformed by electroplating and is one of a homogeneous magnetic polematerial or a magnetic pole material with a graded magnetic structure.13. The method of claim 12, wherein the graded magnetic pole material isformed by current controlled electroplating.
 14. The method of claim 12,wherein the graded magnetic material is formed by sequentially platinglayers of magnetic material from different plating baths.
 15. The methodof claim 12, wherein the magnetic pole material is at least one of FeCo,CoNiFe, NiFeCu, and NiFe.
 16. The method of claim 12, wherein the gradedmagnetic pole material is a multilayer structure comprised of a firstlayer comprising a IT NiFe layer having a thickness from about 25 nm toabout 200 nm on the seedlayer, a second layer comprising a IT NiCu layerhaving a thickness of from about 25 nm to about 100 nm on the firstlayer, and a 0.3T NiCu layer having a thickness of from about 25 nm toabout 100 nm on the second layer.
 17. The method of claim 16, whereinthe first layer is comprised of a high moment alloy comprising at leastone of FeCo or CoNiFe and having a thickness of from about 25 nm toabout 300 nm.
 18. The method of claim 16, wherein the first layer isabsent and the seedlayer is a high moment multilayer magnetic structure.19. The method of claim 1, wherein the write pole has a trapezoidalcross-section with a bottom width W_(b) less than or equal to about 100nm, a top width about 1.25 to about 5 times the bottom width, a height hand an aspect ratio h/W_(b) about 1:1 to about 10:1.
 20. The method ofclaim 1, wherein the seed material outside the pole area is removed byion milling.
 21. The method of claim 20, wherein the ion milling is oneof static ion milling wherein the target is stationary or dynamic ionmilling wherein the target is oscillated through an angle range of lessthan 40°.
 22. A magnetic write pole comprising: a base; a magneticseedlayer on the base; and a magnetic layer on the seedlayer with atrapezoidal cross-section, the magnetic layer having a bottom widthW_(b) less than or equal to about 300 nm, having a top width of about1.25 to about 3 times W_(b), having a height h, and having an aspectratio h/W_(b), of about 1:1 to about 10:1.
 23. The magnetic write poleof claim 22, wherein the magnetic seedlayer is a multilayer seedlayerformed of magnetic and nonmagnetic layers.
 24. The magnetic write poleof claim 23, wherein the magnetic seedlayer comprises a first NiFe layeron the base, a second CoNiFe layer on the first NiFe layer, a third Talayer on the second CoNiFe layer, a fourth NiFe layer on the third Talayer, and a fifth CoNiFe layer on the fourth NiFe layer.
 25. Themagnetic write pole of claim 24, wherein the first NiFe layer has athickness between about 5 Å and about 25 Å, the second CoNiFe layer hasa thickness between about 150 Å and about 350 Å, the third Ta layer hasa thickness between about 5 Å and about 20 Å, the fourth CoNiFe layerhas a thickness between about 15 Å and about 60 Å, and the fifth CoNiFelayer has a thickness between about 200 Å and about 300 Å.
 26. Themagnetic write pole of claim 24, wherein the magnetic seedlayercomprises a sixth corrosion protection layer.
 27. The magnetic writepole of claim 26, wherein the sixth layer comprises Ni₈₀Fe₂₀.
 28. Themagnetic write pole of claim 23, wherein the magnetic layers in themagnetic seedlayer have different magnetizations such that the magneticseedlayer exhibits a magnetization gradient perpendicular to the base.29. The magnetic write pole of claim of claim 22, wherein the magneticlayer on the seed layer is a homogeneous magnetic pole or a magneticpole with a graded magnetic structure.
 30. The magnetic write pole ofclaim 29, wherein the homogeneous magnetic pole material is at least oneof FeCo, CoNiFe, NiFeCu, and NiFe.
 31. The magnetic write pole of claim29, wherein the graded magnetic pole material is a multilayer structurecomprised of a first layer comprising a 1T NiFe layer having a thicknessfrom about 25 nm to about 200 nm on the seedlayer, a second layercomprising a 1T NiCu layer having a thickness of from about 25 nm toabout 100 nm on the first layer, and a 0.3T NiCu layer having athickness of from about 25 nm to about 100 nm on the second layer. 32.The magnetic write pole of claim 31, wherein the first layer iscomprised of a high moment alloy comprising at least one of FeCo orCoNiFe and having a thickness of from about 25 nm to about 300 nm. 33.The magnetic write pole of claim 32, wherein the first layer is absentand the seedlayer is a high moment multilayer magnetic structure.